Browsing by Author "Gok, Cem"

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Biosorption of Uranium(Vi) by Bi-Functionalized Low Cost Biocomposite Adsorbent
(Elsevier, 2011) Aytas, Sule; Turkozu, D. Alkim; Gok, Cem
This paper presents biosorption properties of U(VI) by bi-functionalized biocomposite adsorbent consists of macro marine algae (Jania rubens) and yeast (Saccharomyces cerevisiae) immobilized on silica gel. Removal of U(VI) from aqueous solution by biosorption on biocomposite in a single component system with pH, initial concentration of U(VI), various contact time and temperature was investigated. Experimental equilibrium biosorption data was analyzed by five two-parameter equations, namely; Langmuir, Freundlich, Dubinin-Radushkevich (D-R), Temkin and Flory-liuggins isotherms. Among these isotherm models, the Temkin model fits better with the experimental data compared to others. Thermodynamic parameters, such as the enthalpy (Delta H degrees), entropy (Delta S degrees) and Gibbs free energy (Delta G degrees) were calculated from the slope and intercept of logK(d) vs. 1/T plot. Results suggested that the bi-functionalized low cost biocomposite adsorbent is a suitable biosorbent material to remove uranium ions from diluted aqueous solutions. On the other hand, immobilization of algae and yeast on silica gel was found to improve their interaction properties with uranium ions in biosorption process. (C) 2011 Elsevier B.V. All rights reserved.
Determination and Evaluation of Natural Radioactivity and Heavy Metal Levels in the Aquatic Environment of Trans-Boundary Rivers: Maritza, Tundja and Arda
(Springer, 2014) Aytas, Sule; Erenturk, Sema; Aslani, Mahmut A. A.; Yusan, Sabriye; Turkozu, D. Alkim; Gok, Cem; Oguz, K. Firat
The main problem in the trans-boundary river system is that heavy metal and radioactive pollution can cause long-term effects on ecosystems. Therefore the natural radioactivity and heavy metal levels in the Maritza, Tundja and Arda Rivers, common for Bulgaria and Turkey, were determined for 3 years period (2007-2010). Gross alpha, gross beta and total radium isotopes activities, uranium and heavy metal concentrations of the surface water of the rivers were investigated and also terrestrial gamma and gamma dose rate were measured. The results were compared with reported data from other countries of the world and the recommended international standards. The results gathered in this study may provide background data on the natural radioactive and heavy metal levels of these trans-boundary rivers.
Natural Radioactivity of Riverbank Sediments of the Maritza and Tundja Rivers in Turkey
(Taylor & Francis inc, 2012) Aytas, Sule; Yusan, Sabriye; Aslani, Mahmoud A. A.; Karali, Turgay; Turkozu, D. Alkim; Gok, Cem; Oguz, K. Firat
This article represents the first results of the natural radionuclides in the Maritza and Tundja river sediments, in the vicinity of Edirne city, Turkey. The aim of the article is to describe the natural radioactivity concentrations as a baseline for further studies and to obtain the distribution patterns of radioactivity in trans-boundary river sediments of the Maritza and Tundja, which are shared by Turkey, Bulgaria and Greece. Sediment samples were collected during the period of August 2007-April 2010. The riverbank sediment samples were analyzed firstly for their pH, organic matter content and soil texture. The gross alpha/beta and U-238, Th-232 and K-40 activity concentrations were then investigated in the collected sediment samples. The mean and standard error of mean values of gross alpha and gross beta activity concentrations were found as 91 +/- 11, 410 +/- 69 Bq/kg and 86 +/- 11, 583 +/- 109 Bq/kg for the Maritza and Tundja river sediments, respectively. Moreover, the mean and standard error of mean values of U-238, Th-232 and K-40 activity concentrations were determined as 219 +/- 68, 128 +/- 55, 298 +/- 13 and as 186 +/- 98, 121 +/- 68, 222 +/- 30 Bq/kg for the Maritza and Tundja River, respectively. Absorbed dose rates (D) and annual effective dose equivalents have been calculated for each sampling point. The average value of adsorbed dose rate and effective dose equivalent were found as 191 and 169 nGy/h; 2 and 2 mSv/y for the Maritza and the Tundja river sediments, respectively.
Removal of Th(Iv) Ions From Aqueous Solution Using Bi-Functionalized Algae-Yeast Biosorbent
(Springer, 2011) Gok, Cem; Turkozu, Dogukan Alkim; Aytas, Sule
Composites could be more effective adsorbents than inorganic and organic components individually. In the present study, the red macro marine algae, Jania Rubens and yeast, Saccharomyces cerevisiae immobilized on silica gel were used as a constituent of bi-functionalized biosorbent to remove thorium ions from aqueous solution. Optimum biosorption conditions were determined as a function of pH, initial Th(IV) concentration, contact time, temperature, volume/mass ratio and co-ion effect. The morphological analysis of the biocomposite was performed by the scanning electron microscopy and functional groups in the biosorbent were determined by FT-IR spectroscopy. In order to find the adsorption characteristics, Langmuir, Freundlich, and Dubinin-Radushkevich adsorption isotherms were applied to the adsorption data. The data were well described by Langmuir adsorption isotherms while the fit of Freundlich adsorption isotherms and Dubinin-Radushkevich equation to adsorption data was poor. Using the equilibrium constant value obtained at different temperature, the thermodynamics properties of the biosorption (Delta GA degrees, Delta HA degrees and Delta SA degrees) were also determined. The results show that biosorption of Th(IV) ions onto biocomposite was exothermic nature, spontaneous and more favorable at lower temperature under examined conditions.